CBSE Class 10 Answered

This happens due to change in relative brightness of the outside objects with respect to other bodies. If the lights are on, the objects in the room are much brighter than the outside objects and the glass also reflects much light making it difficult to see the outside objects. When the room-lights are off, the amount of light reflected by the glass or the other objects in the room decreases considerably making the outside body relatively brighter.

This is similar to the case of stars not being visible in presence of the sun while they become visible in the night-time.